*{margin: 0; padding: 0;}
ul{list-style: none;}
li{width:100px; float: left;}
.cl_btoh{clear: both;}

#head{width:1200px; height:50px; line-height: 50px; margin:0 auto; background-color: #303641;}
#head a{color:#ECEFF1;}
#head ul{line-height: 50px;}
#head li{text-align: center;}

#main{height:800px; width:1200px; background-color: yellowgreen; margin: 0 auto; color:#FFFFFF;
text-align: center; line-height: 400px;}

#footer{height:40px; width:1200px; margin: 0 auto; background-color: #3B666B; color:#FFFFFF;
text-align: center; line-height: 40px;}